The present disclosure relates to a developing device and an image forming apparatus including the same, and in particular, to a developing device including a first conveyance chamber and a second conveyance chamber arranged above the first conveyance chamber, the first and second conveyance chambers each having arranged therein a stirring-conveyance member for stirring and conveying a developer, and an image forming apparatus including such a developing device.
In an image forming apparatus, an electrostatic latent image formed on an image carrier, such as a photosensitive body, is developed and visualized as a toner image by a developing device. A known example of such a developing device is a developing device that includes a developing container which contains a developer, a first stirring-conveyance member and a second stirring-conveyance member which stir and convey the developer, and a developing roller (a developer carrier) which carries thereon the developer supplied thereto from the second stirring-conveyance member. The first stirring-conveyance member conveys the developer to one side in an axial direction of the developing roller, and the second stirring-conveyance member supplies the developer to the developing roller, while conveying the developer to the other side (opposite side of the one side).
Now, in recent years, there has been an increasing demand for compact image forming apparatuses, and in particular, in color image forming apparatuses, in which a plurality of developing devices are arranged, there has been a demand for compact developing devices.
In this regard, there is known a developing device that includes a first conveyance chamber in which a first stirring-conveyance member is arranged and a second conveyance chamber which is arranged above the first conveyance chamber and in which a second stirring-conveyance member is arranged. Such a developing device can be made compact in the horizontal direction by arranging the first conveyance chamber and the second conveyance chamber one above the other. Accordingly, it is possible to reduce space for installing developing devices, and thus, to achieve compact image forming apparatuses.
Conventionally, there has also been known a developing device which includes a first stirring-conveyance member and a second stirring-conveyance member which stir and convey a developer, a first conveyance chamber in which the first stirring-conveyance member is arranged, and a second conveyance chamber in which the second stirring-conveyance member is arranged, the first stirring-conveyance member including a rotary shaft, two spiral blades (a double-spiral blade) formed on the outer peripheral surface of the rotary shaft to convey the developer in a first direction, and a reverse spiral blade which is opposite in winding direction to the two spiral blades and arranged downstream of the two spiral blades in the first direction.
In this developing device, when the first stirring-conveyance member rotates, the reverse spiral blade applies, to the developer, conveying force in a direction that is opposite to the direction in which the developer is conveyed by the two spiral blades. This conveying force in the opposite direction applies pressure such that the developer becomes heaped up high on a downstream side in the first conveyance chamber, and thereby, the developer is conveyed from the first conveyance chamber into the second conveyance chamber.